1. Field of the Invention
The invention relates to an apparatus for hardening cylindrical bearing locations on a shaft, in particular a crankshaft, in which transition radii to the adjacent shaft parts are of undercut design. The invention also relates to a process for hardening cylindrical bearing locations of this type.
2. Description of the Related Art
U.S. Pat. No. 6,399,928 has illustrated and described an apparatus for hardening cylindrical bearing locations on a shaft, two independent heating units, each having an inductor, being provided. Each inductor is in this case provided with two heating conductor arms arranged at a distance from one another. Each of the two heating conductor arms has an outer heating conductor branch and an inner heating conductor branch. The bearing surface of the bearing location that is to be hardened is hardened using the inner heating conductor branches and the undercut transition radii are hardened using the outer heating conductor branches. To harden the undercut transition radii, the two inductors are in each case displaced following a radial advance in the axial direction—with respect to the shaft or bearing location that is to be hardened—so that the heating conductor branches can accordingly be introduced into the undercut transition radii. To ensure that there are no unhardened or insufficiently hardened areas in the central region of the bearing surface, the inner heating conductor branches must cover one another in an overlap region as seen in the peripheral direction, but without touching one another. The two heating units with their inductors which operate independently of one another make it possible to dispense with electrical cross-connections between the inductors and the respectively associated heating unit and also in the coolant supply, which are susceptible to faults. However, one drawback of this is that the apparatus is relatively expensive compared to the prior art, on account of the duplication of the heating units with their two inductors. Furthermore, relatively high masses have to be moved during the axial advance of the outer heating conductor arms, which likewise results in a relatively high level of outlay, and is also susceptible to faults.